CN101390429A - Apparatus and method for controlling channel switching in wireless networks - Google Patents

Abstract

The invention provides apparatus and methods for avoiding channel collisions in Wireless Regional Area Networks (WRAN). A medium access controller (MAC) for switching a base station (BS) of a WRAN from a first channel to a second channel at a time t is provided. The MAC includes a switch time delay circuit for delaying said switching with respect to time t by a random delay time.

Description

Apparatus and method for controlling channel switching in wireless network

Cross References to Related Applications

This application claims priority to U.S. Provisional Application 60/757,998, entitled METHOD FOR CHANNEL SWITCH ANDINTER BASE STATION COMMUNICATION IN WIRELESS REGIONAL AREA NETWORK, filed January 11, 2006 in the United States Patent and Trademark Office of the inventors GAO, Wen et al.

technical field

The present invention relates to wireless networks, in particular to methods and devices for controlling channel switching in wireless area networks (WRAN).

Background technique

Demand for broadband communication access is growing. In some cases, it is difficult to provide such access. For example, sparsely populated rural areas and other underserved areas of the world lack the wireline infrastructure to support wireline broadband access. The Institute of Electrical and Electronics Engineers (IEEE) Wireless Area Network (WRAN) Working Group has proposed a standard specification (designated 802.22) for wireless networking to meet the growing demand for wireless broadband access. The IEEE 802.22 WRAN specification describes a WRAN system configured to operate within radio frequency (RF) broadcast bands typically reserved for authorized users. An example of an authorized user in the RF broadcast band is a television broadcast station.

Channel switching is an important capability for WRAN. WRAN transceiver nodes switch operating channels to avoid interference with authorized legacy services in the broadcast band. When existing usage is detected, the WRAN node can switch from a first channel (eg, the channel on which the node establishes a communication link) to a second channel.

Another reason for WRAN channel switching is to maintain quality of service (QoS) on the WRAN communication link. Link quality may be degraded due to factors such as weather, electrical interference, damaged equipment, and other factors. When the link quality degrades, it is sometimes desirable for the WRAN system to change to a different channel in order to maintain the link quality. Channel switching supports the option to establish a new communication link on a second (different) channel if the first channel is degraded.

Another reason for channel switching is the use of a spread spectrum communication technique known as Frequency Hopping (FH). Frequency hopping is another way WRANs can avoid interfering with incumbent services. A frequency hopping WRAN system distributes communications in the time domain over several different frequencies. Each of the multiple frequencies is used only a small amount of time.

Legacy services are allocated relatively narrow frequency bands. Legacy services typically have the right to transmit at sufficiently high power to override WRAN communications. Therefore, any interference caused by the WRAN on a given channel affecting legacy services is transient. Any interference from WRAN is likely to be overwhelmed by incumbent services. At the same time, legacy services suppress only one of the frequencies used by frequency hopping WRAN stations. Therefore, legacy services arriving on licensed channels disturb only a portion of WRAN transmissions.

One channel switching challenge for WRANs is to avoid channel conflicts with other WRANs when switching channels. Collisions may arise between WRAN stations if more than one WRAN station simultaneously selects the same second channel for handover. Therefore, there is a need for an apparatus and method for controlling channel switching in a WRAN system to avoid channel conflicts.

Contents of the invention

Embodiments of the present invention provide an apparatus and system for controlling channel switching in a wireless area network (WRAN).

Description of drawings

In conjunction with the ensuing detailed description, a full understanding of the invention is disclosed in the accompanying drawings in which:

Figure 1 is a schematic diagram of an example WRAN system suitable for deploying embodiments of the present invention;

Figure 2 is a schematic diagram of an example WRAN cell according to an embodiment of the present invention;

3 is a block diagram of a BS according to an embodiment of the present invention;

Figure 4 is a diagram illustrating the WRAN handover problem;

FIG. 5 is a flowchart illustrating the steps of a conventional method for avoiding channel collisions;

Figure 6 is a more detailed block diagram of an embodiment of the invention as shown in Figures 2 and 3;

FIG. 7 is a flowchart illustrating steps of a method for avoiding channel collisions according to an embodiment of the present invention.

Detailed ways

For purposes of illustration, the following terms as defined herein are used.

The term "base station" (BS) refers to a collection of equipment that provides connectivity, management, and control of at least one collection of customer premises equipment (CPE).

The term "customer premises equipment" (CPE) refers to equipment that provides connectivity between WRAN subscribers and BSs.

When referring to a WRAN, the term "cell" is defined to include at least one BS.

The term "node" refers to a group of network elements that provide network-related functionality. For example, a base station includes a node of a WRAN. The CPE includes nodes of the WRAN.

The term "radio" refers to the wireless transmission of signals by modulation of electromagnetic waves whose frequency is lower than that of light.

The term "cognitive radio" refers to a radio transmitter-receiver (transceiver) designed to detect whether at least a specific portion of the radio frequency (RF) spectrum is currently in use.

The term "channel" refers to a designated frequency or designated frequency band used for communication between a sender and a receiver. A particular channel is represented in a variety of ways. The channel number indicates an established channel number used by a medium access controller (MAC). In some embodiments, a channel number represents a physical channel. In other embodiments of the invention, the channel number indicates a logical channel. Channel numbers in one representation scheme can be mapped to other representation schemes by hardware and software in the sender and receiver stations.

The term "downstream" refers to the direction from the BS to the CPE. The term "upstream" refers to the direction from the CPE to the BS.

The term "information" refers to the state of the system of interest.

The term "message" refers to information embodied and organized according to a message format.

Figure 1 WRAN

FIG. 1 shows an example wireless network 10 suitable for deploying the various embodiments of the invention shown in FIGS. 2 , 3 and 6 . Figure 1 shows a network 10, but only as one example of the many possible network configurations suitable for deploying various embodiments of the present invention. According to one embodiment of the present invention, wireless network 10 comprises a wireless area network (WRAN). For example, WRAN is described in "IEEEP802.22/DO.1, Draft Standard for Wireless Regional Area Networks Part22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Unit (PHY) specifications: Policies and procedures for operation in the TV Bands" general specification.

In one embodiment of the invention, the network 10 is generally configured according to the proposed draft IEEE 802.22 specification. Other embodiments of the invention not described in the current draft of the IEEE 802.22 specification are contemplated. These embodiments may or may not be described in future 802.22 specifications. Regardless of the 802.22 specification, the WRAN 10 includes at least one cell 26. The cell 26 comprises at least one base station BS 100. The BS 100 is typically associated with at least one Customer Premises Equipment (CPE) 18. Typically, a cell 26 includes at least one BS 100 and at least one CPE 18. The example WRAN 10 shown in FIG. 1 includes a plurality of cells 26 and 26a-26d. Multiple CPEs 18 make up each cell 26 and 26a-26d. At least one BS (eg, BS 100 of cell 26) is coupled to a backbone (BB) network 211. The BB network 211 constitutes a traditional wired broadband service. BS 100 couples CPE to BB network 211 via a wireless link coupling CPE 18 with BS 100 and via a wired link coupling BS 100 to BB network 211.

In some embodiments of the invention, the service coverage of each cell 26 extends to the point where signals transmitted from the BS 100 can be received by the associated CPE with a given minimum signal-to-noise ratio (SNR). In some embodiments of the invention, the service coverage of some cells 26 overlaps with the service coverage of other cells 26, as shown in FIG. 1 .

A typical example cell 26 includes a BS 100 and a plurality of associated CPEs 18. It should be understood that the number of cells 26, base stations 100, and CPEs 18 shown in FIG. 1 is chosen for ease of illustration and ease of discussion in such permitted specifications. In actual practice, the number of cells 26, BS 100 and CPE 18 of WRAN 10 will vary. The invention is not limited to WRANs comprising any particular number of cells 26, BS 100 or CPE 18.

Alternative configurations of networks suitable for deploying the present invention include WRAN systems with more than one WRAN 10 . In this case, the system of WRAN 10 ideally avoids interfering with each other on the communication channel and avoids existing users interfering with the channel.

Figure 2 Cell

FIG. 2 is a schematic diagram of an example cell 26 of the WRAN 10 of the general type shown in FIG. 1 . Cell 26 includes at least one BS 100 and at least one CPE (eg, CPE 18 and CPE 18a). The example cell 26 shown in FIG. 2 includes a BS 100 and a plurality of CPEs 18. BS 100 includes at least one transmit antenna and at least one receive antenna, indicated by transceiver antenna 203. FIG. 2 shows two example base station transceiver antennas 203 and 204 . The invention is not limited to any particular number of base station antennas. The transceiver antenna 203 is coupled to a transmitter and receiver (transceiver) 244 . The BS 100 also includes a spectrum sensor antenna 205 coupled to a cognitive radio transceiver 245.

BS 100 also includes BS controller 288 and backbone interface 214. Backbone interface 214 couples at least one backbone network to BS controller 288 . Figure 2 shows two examples of backbone networks. A first example of a backbone network includes a traditional wireline connection 210 to the Internet 211 . A second example of a backbone network includes satellite communication links 237 to communication satellites 212 .

In one embodiment of the invention, BS 100 provides wireless extension of broadband service carried by at least one backbone network (e.g., satellite broadband network 212) to users in geographic areas where satellite 212 broadcast service is not directly extended to CPE 18. According to an example embodiment, the backbone interface 214 of the BS 100 includes an interface between a wireless backbone network and a wired backbone network. Other examples of wired backbone networks suitable for the implementation of the present invention include cable networks, fiber optic networks, public telephone networks, and the like. BS controller 288 is coupled to transceiver 244 to control the operation of transceiver 244 to communicate with at least one CPE 18 of cell 26. Accordingly, at least one communication link (e.g. 250) is established between at least one backbone network (e.g. 211) and at least one CPE 18 of the cell 26. In an example embodiment of the invention, the base station 100 and the plurality of CPEs 18 are arranged in a point-to-multipoint network configuration. In this example, a BS 100 constitutes a point, and multiple CPEs 18 constitute a multipoint.

In one embodiment of the invention, the transceiver 244 of the BS 100 of the WRAN 10 operates on the UHF/VHF TV band between 54 MHz and 862 MHz. According to other embodiments of the invention, the BS 100 of the WRAN 10 uses other television bands for communicating with the CPE 18. In some embodiments of the invention, the BS 100 of the WRAN 10 relies on the guard band for communicating with the CPE. Regardless of the channel and frequency on which the WRAN 10 or BS 100 operates, the ideal WRAN 10 avoids interfering with the use of any communication channel by existing users (ie authorized users).

The example CPE 18a includes at least one CPE transmit/receive antenna 216 coupled to a CPE transceiver 280. CPE controller 299 is coupled to transceiver 280 . The CPE controller 299 is also coupled to the user application unit 241 . For example, user application unit 241 includes a personal computer 242 and associated hardware and software. A CPE controller 299 is coupled between the user application unit 241 and the transceiver 280 to provide a communication link 250 between the user application unit 241 and at least one backbone network of the BS 100.

BS 100 communicates with a CPE (eg, CPE 18a) via air communication link 250. A link 250 is established between at least one BS antenna (eg, 204 ) and a CPE antenna 216 . Similar communication links between CPE 18 and BS 100 are indicated by dotted lines 251, 252, 253, 254, 255, and 256.

In one embodiment of the invention, the BS 100 broadcasts downlink transmissions to the example CPE 18a. In one embodiment of the invention, downlink transmissions of the BS 100 are received by all of the CPEs 18, 18a making up the cell 26. In one embodiment, a single uplink from CPE 18 to BS 100 is shared by multiple CPEs of cell 26. In some embodiments, the uplink channel comprises a multiple access channel. In one embodiment of the invention, each BS 100 controls its uplink transmissions by allowing access according to specified Quality of Service (QoS) requirements.

In one embodiment of the invention, the controller 299 of the example CPE 18a comprises a Media Access Controller (MAC). In some embodiments, the controller 299 employs conventional multiple access methods to share access to the communication link between multiple CPEs and the BS 100 with other CPEs.

The three conventional methods for medium access control applicable to BS 100 and CPE 18 according to various embodiments of the present invention are frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). In an FDMA embodiment, the medium is divided into portions of the frequency spectrum called channels. In a TDMA embodiment, access to the medium is divided into sections comprising time slots. In a CDMA embodiment, the assigned nodes are divided by the codes of the same channel by which they can share the medium.

One embodiment of the present invention employs Orthogonal Frequency Division Multiple Access (OFDMA) techniques. In one OFDMA embodiment of the invention, the medium is partitioned in time-frequency space. This is achieved by allocating CPEs along both the OFDM signal index and along the OFDM subcarrier index. In this embodiment, BS 100 transmits symbols by using subcarriers that remain orthogonal to those of other CPEs of cell 26. Some embodiments of the invention allocate more than one subcarrier to a CPE, for example to support high-rate applications.

Other embodiments of the invention include alternative multiple access arrangements and schemes. Some embodiments of the invention contemplate employing a combination of at least two multiple access schemes for dividing the frequency spectrum into portions. Regardless of the access scheme employed by various embodiments of the invention, the present invention provides systems and methods for avoiding channel collisions when switching channels.

According to some embodiments of the invention, the BS 100 optionally includes a spectrum sensor antenna 205. Spectrum sensor 205 is coupled to spectrum management module 260 . In one embodiment of the invention, spectrum management module 260 (further shown at 260 in FIG. 3 ) includes a cognitive radio system (best shown at 245 in FIG. 3 ). In one embodiment of the invention, the example CPE 18a provides distributed spectrum sensing capabilities for the BS 100 of the cell 26. In this embodiment, the CPE 18 is equipped with a spectrum sensor antenna and a spectrum manager in a similar manner as the BS 100.

In this embodiment, the CPE is configured to perform local spectrum measurements. The CPE 18 reports the local measurements to the BS 100. BS 100 collects data from CPE 18. The BS 100 determines whether an incumbent user (e.g., an authorized user) is present on the sensed portion of the RF spectrum based on information collected from the CPE along with its own BS 100 measurements.

Unlike a typical BS, the BS 100 of FIG. 2 also includes a random delay circuit (RDC) 659 (also shown at 659 in FIG. 6). In one embodiment of the invention, random delay circuit 659 forms part of BS controller 288 . In an alternative embodiment of the invention, delay circuit 659 forms part of transceiver 244 . It should be appreciated that various specific hardware and software implementations of the functionality of the BS 100 shown in FIG. 2 are possible. Accordingly, the random delay circuit 659 may be configured in various combinations of hardware and software components of the BS 100. Regardless of what hardware the random delay circuit 659 is associated with, the circuit 659 avoids collisions on the second channel when the BS 100 switches from the first channel to the second channel.

The BS 100 of the WRAN 10 and each CPE 18 constitute each node of the WRAN 10. In one embodiment of the invention, all nodes are fixed nodes. According to an alternative embodiment of the invention, at least one node of the network 100 is mobile.

According to the embodiment shown in FIG. 2, the wireless transmission medium coupling the CPE 18 to the corresponding BS 100 includes air. However, the invention is not limited to applications in air medium. Other media for propagating communication signals between nodes of wireless network nodes are possible. For example, it is known to propagate signals through liquid media such as water, as well as gases other than air and through approximate vacuums such as space.

Regardless of the medium through which signals in a cell 26 of the network 10 propagate, each node of a cell 26 shares access to the medium with at least one other node of the cell 26 . Accordingly, embodiments of the invention include protocols and circuitry for sharing access to the medium by nodes of cell 26 of network 10 .

Figure 3 base station 100

FIG. 3 is a high-level block diagram of the BS 100 shown in FIGS. 1 and 2. FIG. 3 depicts a BS 100 represented by the Open Systems Interconnection Reference Model (OSI--RM) according to the present invention. BS 100 includes at least one Physical-Media Access Control Interface (PHY/MAC) module, such as module 306. Other embodiments of the present invention include multiple PHY/MAC modules (eg, 302, 304, and 306), as shown in FIG.

The PHY/MAC modules (302, 304, 306) include medium access control units (MAC 310, 311, 312) and physical units (PHY 320, 321, 322). An example MAC 312 of the PHY/MAC unit 306 includes a Cognitive Media Access Controller (CMAC) 312. CMAC unit 312 includes a transceiver controller, such as controller 288 . Transceiver controller 288 of MAC 312 is coupled to transceiver 244 of PHY unit 322 for controlling channel switching of BS 100.

PHY unit 322 includes transceiver 244 . PHY unit 322 also includes conventional electronic, mechanical, and programmatic interfaces (not shown) to the air transmission medium including portions of the RF spectrum used by BS 100 to communicate with CPE 18, according to an embodiment of the invention. The example PHY unit 322 includes a transceiver 244 that is coupled to a radio frequency (RF) antenna 204 . Transceiver 244 transmits bits over the air medium on a communication link (eg, shown at 250 in FIG. 2 ) between BS 100 antenna 204 and CPE 18 antenna (eg, antenna 216 of FIG. 2 ).

PHY unit 322, together with MAC unit 312, defines the interface between the physical components of BS 100 and the medium access control functions. According to an embodiment of the present invention, the PHY/MAC module 306 complies with the draft IEEE 802.22 standard specification. An example PHY/MAC unit 306 establishes a communication link between the BS 100 and the CPE 18 (best shown in FIG. 2 ). According to some embodiments of the present invention, at least one PHY/MAC module (302, 304, 306) also establishes communication between BS 100 and a second BS (example shown in FIG. 4) to provide inter-base station communication.

According to an embodiment of the invention, the BS 100 also includes a backbone network interface 388. The backbone network interface 388 includes a bridging unit 333 and a protocol unit 330 . Bridge unit 333 and protocol unit 330 define the interface between BS 100 and a wired or other wireless network. In turn, PHY/MAC unit 306 of BS 100 couples CPE 18 to the backbone network via backbone network interface unit 388.

The CMAC unit 312 includes a controller 288 coupled to the transceiver 244 of the PHY unit 322 to control channel selection and switching of the BS 100, according to an embodiment of the invention. Transceiver 244 is coupled to antenna 204 . A communication link (eg 250 shown in Figure 2) is established through the air medium between the CPE antenna (eg 18a in Figure 2) and the BS 100 antenna 204. Accordingly, BS 100 provides CPE 18 with access to the backbone network. The controller 288 includes a random delay circuit 659 . According to some embodiments of the present invention, random delay circuit 659 includes random wait timer 445 and random number generator 447 . The configuration and operation of the controller 288 is discussed in further detail with respect to FIG. 6 .

For ease of discussion, Figure 3 shows three PHY/MAC modules 302, 304, and 306. However, as indicated by the dashed lines, the present invention is not limited to the number of PHY/MAC modules in the BS 100. Embodiments of the present invention may also include more or fewer PHY/MAC modules than shown in FIG. 3 . Other embodiments of the BS 100 may be configured to add PHY/MAC modules as the needs of the BS increase. Therefore, the architecture of the BS 100 shown in FIG. 3 may be increased or decreased according to some embodiments of the present invention.

PHY 322 also incorporates a cognitive radio transceiver (shown separately at 245), according to an embodiment of the invention. According to some embodiments of the invention, CMAC 312 cooperates with cognitive radio (CR) 245 to form cognitive radio MAC (CMAC) 312. CR 245 is configured to sense at least a portion of the radio frequency spectrum. An example spectrum sensing technique employed by the CR 245 is carrier sensing. However, the present invention does not rely on a particular spectrum sensing technique. Other spectrum sensing techniques are suitable for use with the present invention. In a CMAC embodiment, CR 245 enables BS 100 to determine communication channel conditions, such as channel occupancy, link quality, and other channel parameters related to the RF spectrum.

In some embodiments of the invention, CMAC 312 is configured to control transceiver 244 based on spectral information provided by CR 245. In response to sensed channel conditions, CMAC 312 switches transceiver 244 into (or out of) a portion (eg, channel) of the RF spectrum. One reason for the handover is to avoid interference with licensed incumbent users of the RF spectrum.

Some CMAC embodiments of the present invention support the following services: unicast (addressed to a single CPE), multicast (addressed to a group of CPEs), and broadcast (addressed to all CPEs in a cell). In particular, for some embodiments capable of spectrum measurement activities, multicast management connections are employed. Some embodiments of the invention provide clustering algorithms to be implemented and measurement loads to be shared. These algorithms will vary by vendor and application.

Various CMAC embodiments implement combinations of access schemes that control contention between CPEs for access to the BB network 388 . Meanwhile, CMAC 312 provides bandwidth suitable for each CPE application. CMAC 312 does this through at least one of four different types of upstream scheduling mechanisms. In some CMAC embodiments, these mechanisms are implemented by using at least one of unsolicited bandwidth grants, polling, and contention procedures. Some embodiments of BS 100 and CMAC 312 employ polling to simplify access to BB network 388.

The polling operation ensures that the CPE application receives service on a deterministic basis. For example, real-time applications like voice and video sometimes prefer consistent based services. At other times, these applications prefer a very tightly controlled schedule. Conversely, data applications are typically more delay tolerant than voice and video applications. Therefore, competing techniques are typically used in data applications. This avoids individual polling of the CPE. A further advantage of competition is the conservation of resources. Some embodiments of the invention avoid long polling for CPEs that have been disabled. Some CMAC 312 embodiments of the present invention dynamically create, delete, and change competitions as needs increase.

spectrum manager

According to an embodiment of the present invention, SM 260 provides spectrum management capabilities to WRAN 10. Spectrum manager 260 supports the Cognitive Radio (CR) MAC (CMAC) embodiment of the present invention. According to some embodiments of the invention, SM 260 is implemented by a programmable logic device. Other hardware and software devices are contemplated for implementing the SM 260. Thus, the present invention is not dependent on any particular hardware or software implementation of SM 260.

In some embodiments of the invention, SM 260 is coupled to cognitive radio 245 and includes a sensor, such as antenna 205. For an exemplary embodiment of the invention, antenna 205 is physically located near BS 100. Accordingly, spectrum antenna 205 senses parameters of the BS 100 spectrum and the nearby operating environment. The CR 245 analyzes spectral parameter changes based on the information sensed and provided by the antenna 205. For example, examples of parameters sensed by antenna 205 and processed by SM 260 (processor, not shown) include parameters selected from the group consisting of: radio frequency spectrum activity, interference levels within the radio frequency spectrum, CPE Behavior, and WRAN state information, but these are few examples.

In one embodiment of the invention, spectrum manager 260 of BS 100 maintains candidate channel list 360. In an embodiment of the invention, candidate channel list 360 is stored in memory (also represented by 360). Suitable memory devices for storing candidate channel list 360 include, but are not limited to, conventional random access memory (RAM) types. In other embodiments of the present invention, the candidate channel list 360 includes other storage media for storing and updating channel list information.

An example candidate channel list includes at least one frequency (e.g., channel [CHselect] 347) available for BS 100 handover. In one embodiment, candidate channel list 360 is compiled based at least in part on sensed spectral parameters as described above. In one embodiment of the invention, SM 260 associates one of high preference, medium preference and low preference to at least one candidate channel constituting BS 100's candidate channel list 360.

In some embodiments of the invention, SM 260 is provided with information such as Geographic Spectrum Status Information (GSSI) provided by the government. The SM 260 compiles the candidate channel list 360 using the GSSI information. In this case, the GSSI provides at least a portion of the input information for dynamic frequency selection (DFS) by the BS 100. In one embodiment of the invention, the GSSI is obtained by the base station node 100 via the backbone interface 388 . In other embodiments of the invention, BS 100 receives GSSI via an over-the-air communication link provided, for example, by antenna 204 and transceiver 244.

According to one embodiment of the present invention, at least one BS 100 of the WRAN 10 includes a GPS (Global Positioning System) receiver (not shown). The GPS receiver is configured to determine the geographic location of the BS 100. The BS 100 location information determined by the GPS receiver is forwarded by the BS 100 to the central server. Suitable central servers include, for example, servers regulated by the FCC, the Federal Communications Commission of the United States. The central server responds by providing BS 100 with information about TV unoccupied channels in BS 100's area. In such embodiments, candidate channel list 360 is based at least in part on information received by BS 100 in response to sending BS 100 location information.

An alternative embodiment of the invention is implemented based on local spectrum sensing by at least one CPE 18 of a cell 26 of the WRAN 10. In local spectrum sensing embodiments, CPE 18 includes at least one local spectrum sensor configured to sense channels available to the CPE. According to some embodiments of the invention, BS 100 employs various combinations of GPS, local spectrum sensing by CPEs, and other methods to determine the channels that make up candidate channel list 360.

In an embodiment of the present invention, spectrum manager 260 also includes a processor (not shown) coupled to cognitive radio 245 for performing user-specified spectrum analysis algorithms on parameters sensed by sensors 205 . For example, in one embodiment of the invention, SM 260 is configured to detect interference conditions (eg, to legacy users or other 802.22 cells) based on sensed parameters. In this case, SM 260 provides a signal to MAC 312 to indicate detection of the jamming condition. MAC 312 initiates appropriate actions by BS 100 to resolve the conflict situation.

In some cases, the appropriate action for the BS 100 is to perform a channel switch. Here, the channel on which the BS 100 has established communication and is currently used by the BS 100 is called a current operating channel (Cop). Thus, in some embodiments of the invention, the first channel comprises the currently operating channel. The second channel is the channel to which the BS 100 wishes to switch. Therefore, in some embodiments of the invention, the second channel comprises a candidate channel [CHselect].

Embodiments of the present invention employ dynamic frequency selection (DFS) techniques to select a channel for switching to to avoid interfering with incumbent users using the current operating channel. The DFS technique selects an alternative channel [CHselect] in response to channel conditions on the operating channel. In some cases, the sensed parameter is indicative of the arrival of an incumbent user on the channel of operation. In this case, the SM dynamically responds to the changes by selecting a new channel [CHselect] for the operation of the BS 100.

To avoid channel collisions, some embodiments of the invention support Frequency Hopping (FH). Frequency hopping is a method of transmitting radio frequency signals by switching the radio frequency carrier between multiple frequency channels. For example, frequency hopping is employed to avoid periods of in-band silence. Another application of frequency hopping is to provide better quality of service (QoS) for certain types of traffic (such as voice traffic). The present invention is applicable to each of these and other frequency hopping applications.

To switch channels (ie frequency hopping), SM 260 selects CHselect based on channel selection criteria. Channel selection criteria include, but are not limited to, the number of CPEs associated with the BS, the average CPE distance from the BS, and the type of traffic on available channels. In response to SM 260, MAC 312 initiates a channel switch to BS 100 via transceiver controller 288 of MAC 312. According to one step in an example handover operation, MAC 312 provides CHselect to transceiver 244 via controller 288.

According to one frequency hopping embodiment of the present invention, BS 100 maintains at least two channels for communicating with CPEs. The first channel comprises the operating channel Cop. The second channel includes a candidate channel Cca. BS 100 operates on an operating channel Cop. However, when the BS 100 senses the operating channel Cop, the BS 100 switches to the candidate channel Cca. In some embodiments of the invention, the BS 100 also senses neighboring channels of the operating channel Cop during the sensing operation. According to one embodiment of the present invention, when a BS 100 wants to sense its current operating channel Cop, the BS 100 sends a Channel Switch and Sensing message (CSS) to the associated CPE 18.

The BS 100 switches to the candidate channel Cca for sending data to the CPE and for other signaling operations. At the same time, the BS 100 senses the operating channel Cop. After sensing the Cop, if there are no existing users or other BSs operating in the Cop, the BS 100 switches back to the operating channel Cop. However, in some cases, BS 100 and a different BS (not shown) may frequency hop to the same channel Cop. For example, before BS 100 and another BS are able to detect a collision, both BSs may frequency hop to the same Cop. In this case, the collision occurs on channel Cop. According to an embodiment of the present invention, controller 288 of CMAC 312 avoids this type of collision problem.

Subunits 330, 333

As shown in FIG. 3, at least one of the MACs 310, 311, and 312 is coupled to at least one backbone network through a backbone interface 388. Backbone interface 388 includes higher level units 330 and 333 of BS 100. More than one network element technology may be supported by the backbone interface 388 of the BS 100. According to an embodiment of the invention, at least one higher level unit of BS 100 implements an Internet Protocol (IP) communication link. Thus, according to some embodiments of the invention, backbone interface 388 couples BS 100 to the Internet. In one embodiment of the invention, backbone interface 388 is coupled to an internet service provider (ISP) backbone network via an Ethernet cable. Like this, the Internet service of accessing Internet 111 by CPE 18 (shown in Fig. 1 and Fig. 2) is provided by BS 100.

In other embodiments of the invention, backbone interface 388 wirelessly couples BS 100 to (eg, satellite 212 of FIG. 2 ) via a satellite communication link established through backbone interface 388 and satellite transceiver equipment. Other examples of transmission media comprising backbone interface 388 include, but are not limited to, fiber optic coupling and coupling through microwave point-to-point transmission equipment.

channel collision avoidance

Figure 4 depicts two example base stations BS 401 and BS 402 to illustrate a collision situation. The first BS 401 and the second BS 402 perform actions described below at times indicated on the respective timelines 410 and 420. For timelines 410 and 420, time t progresses in the direction of the arrow.

The period of dynamic frequency hopping (DFH) operation of BS 401 includes a first period of time indicated along timeline 410 between markers 421 and 422. A second DFH operation period of the BS 401 is indicated between marks 422 and 423 . Example DFH operating periods for BS 402 include the time period indicated along timeline 420 between markers 451 and 452. Between markers 452 and 453 is indicated a second DFH operation period for BS 402.

At the beginning of timeline 410, BS 401 is operating on a channel (not indicated). At an example time indicated at 431, the BS (401) verifies that channel A is available. At time 421, BS 401 begins operating on channel A. While BS 401 is operating on channel A, BS 402 senses channels [0, A-n] and [A+n, N], where n is a single channel increment and N is the number of channels to be sensed. At the beginning of timeline 420, BS 402 is operating on example channel X (not indicated). At the example time indicated at 441, BS 402 verifies that a different channel (channel D) is available. At example time 451, BS 402 begins operating on channel D. While BS 402 is operating on channel D, BS 402 senses on channels [0,D-n] and [D+n,N].

BS 401 detects the availability of channel C at time 433. BS 402 detects the availability of channel C at time 442. As shown in Figure 4, the channel C verification time of BS 401 is close in time to the channel C verification time of BS 402. In this case, BS 401 and BS 402 would both be able to independently select channel C for use in their next DFH operation periods (422 and 452, respectively). The DFH operation periods of BS 401 and BS 402 overlap each other. If both BS 401 and BS 402 hop to channel C during their overlapping DFH operation periods, then a collision occurs on channel C. The occurrence of a channel usage conflict is due to the fact that neither BS 402 nor BS 401 is aware of the frequency selected by the other BS. Typically, such channel usage information is only detected by cognitive radios when potentially conflicting channels are actually used.

Figure 5 shows a proposed solution to this conflict problem. This solution relies on sending and receiving channel information via Dynamic Frequency Selection (DFS) announcements. A DFS announcement must be sent from the handover BS of the WRAN to other BSs of the WRAN to inform the other BSs and the WRAN of the selected channel. 5 illustrates an example method for a first BS of a WRAN system to select a frequency and switch to a new channel for operation. The method starts at step 501 under normal operation of the first BS. The first BS selects the next hopping frequency, as shown in step 503 .

In step 505, the first BS notifies other BSs (eg, another WRAN's BS) of its selected next frequency. In some embodiments of the invention, the announcement is made by the first BS sending a message to other WRANs. After sending the announcement in step 505, the first BS waits for a predetermined delay period, as shown in steps 507 and 513. In one embodiment of the invention, during the waiting step 507, a fixed delay period is counted by a delay timer. While the delay timer is counting the fixed delay, the first BS listens for colliding channel announcements from other BSs, such as BSs from other WRAN stations. If the delay timer expires in step 513 without the first BS receiving a collision notification in step 509 , the first BS prepares to jump (handover) to the selected next channel, as shown in step 515 . In this case, the method ends at 517.

A collision is detected at step 509 if the first BS receives a DFS announcement from the second BS announcing the same next frequency selected by the first BS. Since both BSs have selected the same frequency for hopping, a collision will occur if both BSs hop to their advertised frequencies.

In this case, the method proceeds to step 511 . In step 511, the first BS compares its own DFS advertisement timestamp with the second BS's DFS advertisement timestamp. If the second BS timestamp is later than the first BS timestamp, the first BS enters its selected next frequency in the next DFS operation period after the waiting period expires. If the second BS timestamp is earlier than that of the first BS, the first BS returns to step 503 to select a different next frequency for hopping. However, the method repeats for the newly selected next frequency.

The method shown in Figure 5 has disadvantages. Successful adoption of this approach relies on neighboring BSs reliably receiving and decoding each other's DFS advertisements. Sometimes conditions interfere with the reliability of sending and receiving DFS advertisements. If this happens, there is a possibility of a collision between the first BS and the second BS on the channel. Therefore, systems and methods that avoid such collision problems without relying on message transmission between BSs are desired.

Solution to the channel conflict problem

A solution to the channel collision problem described above is provided by an apparatus according to an embodiment of the present invention. Figure 6 further illustrates these embodiments. Embodiments of the present invention do not rely on message transmission and reception between BSs to avoid channel conflicts. FIG. 6 shows further details of the invention shown in FIGS. 2 and 3 . As described above with respect to FIG. 3 , FIG. 6 shows an embodiment of the invention constituting at least one WRAN 10. WRAN 10 includes at least one cell. A cell includes at least one BS 100. BS 100 includes at least one PHY/MAC module 306 coupled to at least one backbone network 388. PHY/MAC module 306 is also coupled to at least one transmit/receive antenna 204 for communicating with at least one CPE via an air interface (best shown in FIG. 2 ). According to an embodiment of the present invention, the PHY/MAC module 306 is configured to communicate with other BSs of other WRAN cells.

PHY/MAC module 306 includes at least one PHY unit 322 . PHY unit 322 includes at least one transceiver 244 coupled to at least one RF transceiver antenna 204 . Transceiver 244 of PHY 322 includes analog section 614 and digital baseband section 616 . The transceiver 244 is operable to transmit and receive radio frequency signals over at least a portion of the radio frequency spectrum via a wireless transmission medium (eg, air). Analog unit 614 includes a typical radio frequency transmitter front end. For example, the analog unit 614 provides conventional front-end circuitry, such as signal amplifiers, modulators, and demodulators, for RF carrier signals transmitted and received via the antenna 204 .

In one embodiment of the invention, the analog unit 614 is operable to transmit and receive radio signals in full-duplex mode. In an alternative embodiment of the invention, the analog unit 614 is operable to transmit on a transmit channel and receive on a receive channel. In this embodiment, the transmission channel and the reception channel are different channels.

Transceiver 244 - Receive Mode

For example, a signal is sent from the CPE 18 (shown in FIG. 2 ) to the BS 100. As shown in FIG. 6, in receive mode, BS 100 receives signals from CPEs and provides information represented in the received signals to backbone network 388. To accomplish this, transceiver 244 receives a modulated RF signal from antenna 204 . The transceiver 244 provides the down-converted analog signal to the baseband unit 616 . The baseband unit 616 receives the down-converted analog signal from the analog unit 614 and converts the analog signal to a digital signal.

According to the OFDM implementation of the present invention, the transceiver 244 receives OFDM signals. The time domain signal is processed by a fast Fourier transform (not shown) of the transceiver 244 to transform the time domain signal into the frequency domain where subchannel data is extracted and QAM value decoding is performed.

In one embodiment of the invention, baseband unit 616 receives a single input baseband signal from analog unit 614 . The baseband unit 616 converts the analog signal into a digital signal. Baseband unit 616 typically includes a baseband processor (not shown). According to an embodiment of the invention, the baseband processor processes the single input digital baseband signal as multiple subband input digital baseband signals to provide a single bit stream to the CMAC 312 at output 605. In one embodiment of the invention, baseband unit 616 includes a digital filter (not shown). The digital filter separates the digital baseband signal into subband digital baseband signals. The output 605 of the baseband unit 616 is coupled to the CMAC 312. CMAC unit 312 provides signals to backbone interface 388 .

send operation

In the embodiment shown in FIG. 6 , CMAC unit 312 includes transceiver controller 288 . During transmit operations, digital baseband unit 616 receives an output communication bitstream from CMAC 312. Baseband unit 616 encodes the communication bitstream. The baseband unit 616 provides digital baseband signals to the analog portion 614 of the transceiver 244 .

Various embodiments of PHY unit 322 and transceiver 244 implement conventional Orthogonal Frequency Division Multiplexing (OFDM) techniques. In these embodiments, digital baseband unit 616 is configured to encode digital data provided by CMAC 312 in a plurality of subchannels. In one embodiment of the present invention, the subchannels include subchannels defined in the IEEE 802.22 WRAN specification. In one embodiment of the invention, PHY3 22 also includes a modulator (not shown) configured for conventional quadrature amplitude modulation (QAM). In this case, magnitude and phase together represent the encoded data.

In one embodiment, the CMAC 312 subchannel data is processed by an inverse fast Fourier transform unit (not shown) of the PHY 322 to combine the subchannel data in a time domain signal. The time domain signal covers a frequency bandwidth substantially equal to the sum of the subchannel spacings or bandwidths of each of the subchannels. The time-domain signal is then transmitted by antenna 204 on the operating frequency (Cop) of BS 100.

In an embodiment of the present invention, the CMAC 312 initiates a switch through the transceiver 244 from the currently operating channel to the next channel. In accordance with an embodiment of the invention, the mixers of transceiver 244 are adjusted in response to signals provided by CMAC 312 to switch channels.

Cognitive MAC

According to an embodiment of the invention, the MAC 312 of the PHY/MAC module 306 includes a Cognitive MAC (CMAC) unit. According to some embodiments of the invention, CMAC unit 312 is coupled to cognitive radio 245 . In other embodiments of the invention, the transceiver 244 of the PHY 322 comprises a cognitive radio transceiver. As described above with respect to FIG. 3, in one embodiment of the invention, CR 245 includes a spectrum manager. In the embodiment shown in FIGS. 3 and 6 , CR 245 maintains a candidate channel list 360 .

CMAC 312 includes transceiver controller 288 coupled to transceiver 244 of PHY 322 for controlling channel switching of transceiver 244. In one embodiment of the invention, the transceiver controller 288 includes a random delay circuit (RDC) 659 . In one embodiment of the invention, RDC 659 includes random wait timer 445, random number generator 447 and processor 603.

In an example operation, the CR 245 senses a portion of the RF spectrum. If the CR 245 detects an existing user or other WRAN BS in the current operating channel (Cop) of the BS 100, the BS 100 selects a channel (CHselect) 347 from the candidate channel list 360. According to some embodiments of the invention, CHselect 347 is randomly selected from the list of channels making up candidate channel list 360. According to an alternative embodiment of the present invention, CHselect 347 is selected based on a user-defined selection algorithm executed by the processor of spectrum manager 260 (best shown in FIG. 3 ).

No matter how CHselect 347 is selected, once Chselect is selected, RDC 659 determines a random waiting time t _Rwait . In one embodiment of the invention, RDC 659 includes Random Number Generator (RNG) 447 . In this case, the processor 603 of the RDC 659 determines t _Rwait based on the random number provided by the random number generator 447 . According to one embodiment of the present invention, the CMAC determines t _Rwait based on the random number provided by the RNG 447 and further based on the minimum waiting time [t _min ]. In one embodiment of the invention, [t _min ] is determined as the time at which the channel switch announcement is to be sent from the BS 100 to its associated CPE.

In other embodiments of the invention, CMAC 312 determines t _Rwait based on a random number provided by RNG 447 and a maximum waiting time [t _max ]. In some embodiments of the invention, the processor 603 selects t _Rwait based on a random number generated by the RNG 447 and also chooses it to fall within the window defined by [t _min ] and [t _max ]. According to an embodiment of the present invention, as the time of timer 445 expires, RDC 659 starts wait timer RW T445 with t _Rwait .

Before the BS 100 switches to CHselect, the cognitive radio 245 senses CHselect for legacy signals and signals from other WRAN systems arriving after the most recent update of the channel candidate list 360 . If the channel CHselect is still free/available at the expiration of _tRwait , the controller 288 provides a signal to the transceiver 244 to change the channel from Cop to CHselect. However, if the CR 245 detects a legacy signal or other WRAN system in CHselect, the CMAC 312 selects another channel CHselect from the candidate channel list 360 (or selects its previous Cop if the legacy signal does not occupy the previous Cop) .

According to an embodiment of the invention, CMAC 312 provides control signals for adjusting characteristics of analog circuitry 614 and baseband unit 616 to switch transceiver 244 from a first channel to a second channel. For example, the center frequency and bandwidth of the analog unit 614 and the characteristics of the digital baseband unit 616 are adjusted by the CMAC 312 to switch from the operating channel (Cop) to the selected channel (CHselect).

According to an embodiment of the present invention, CMAC 312 includes circuitry to implement conventional functions exemplified by media access controllers according to the IEEE 802.11 standard. However, in contrast to conventional media access controllers, the CMAC 312 of the present invention includes a transceiver controller 288 that implements the various functions of the present invention. The controller 288 includes a random delay circuit 659 . Random delay circuit 659 includes random number generator 447 , processor 603 and timer 445 . The controller 288 avoids channel conflicts when the BS 100 switches from the first channel to the second channel.

Embodiments of the present invention avoid collisions without sending or receiving DFS advertisements. The flowchart of Figure 7 illustrates the method according to this embodiment of the invention. The method according to an embodiment shown in Fig. 7 avoids channel collisions without notifying neighboring base stations of channel changes. The steps of the method are as follows. In step 701, the BS 100 of the example WRAN 10 operates in an operating channel (Cop). At step 702, a cognitive radio including a spectrum manager senses an operating channel to determine whether channel switching criteria are met. An example of a channel switching criterion is the sensed arrival of a legacy signal on the operating channel (Cop). If the arrival of an existing signal is sensed on the operating channel, the BS 100 selects a new frequency (CHselect) frequency for handover in step 704.

In step 705, a random delay time is generated. In one embodiment of the present invention, the step of generating a random delay time is performed by a step of generating a random number. In one embodiment of the method of the present invention, the random delay time for step 705 is based on a random number generated by a random number generator. In step 706, the BS 100 waits for the random delay time to expire. In one embodiment of the present invention, during the waiting step 706, the BS initiates a step of sensing the selected channel (CHselect)) to determine whether the selected channel is still available according to the expiration of a random delay time.

In one embodiment of the invention, the waiting step is performed by the step of setting a delay timer. As indicated in step 706, the BS 100 waits for the random delay timer until the timeout indicated in step 711. If the selected channel (CHselect) is in use, the BS 100 terminates step 709 and jumps to step 704 to select a new frequency for handover. For the new frequency, steps 706, 707 and 708 are repeated.

In one embodiment of the invention, the BS 100 senses the selected channel (CHselect) to determine whether the selected channel is still available. In one embodiment of the present invention, the BS 100 performs the step of communicating on the operating channel Cop concurrently with the step of sensing. In an alternative embodiment of the invention, the BS 100 senses the selected channel (CHselect) at a time before the random wait timer expires. If the selected channel (CHselect) is in use, the BS 100 jumps to step 704 to select a new frequency for handover. For the newly selected frequency, steps 706, 708 and 707 are repeated.

If the selected channel (CHselect) is sensed at step 707, and it is determined that it is not occupied, then when the random wait timer expires, the BS 100 switches to the selected channel, and the process ends at step 713. Because each WRAN in the system of the present invention generates random numbers to provide handover delay, the possibility of two BSs handing over to the same channel at the same time is negligible. Therefore, it is possible for a BS with a longer random delay time to detect the presence of a BS with a shorter random delay time during the sensing step 707 .

In one embodiment of the present invention, the BS 100 senses the selected channel (CHselect) at a time after the random wait timer expires. In an alternative embodiment, the BS 100 announces the selection of CHselect on the operational channel Cop.

The embodiments of the present invention described above may be implemented as a combination of hardware and software elements. Since other modifications and variations as altered to meet particular operating needs and circumstances will be apparent to those skilled in the art, the invention should not be considered limited to the examples chosen for the purposes of the disclosure and covers All changes and modifications constitute departures from the true spirit and scope of the invention. Having thus described the invention, what is desired to be protected by Letters Patent is set forth in the appended claims.

Claims (25)

1. A channel switching delay circuit used in a node of a wireless communication network, said node comprising a medium access controller MAC, said medium access controller MAC being coupled to a transceiver, to transmit and receive said transceiver at time t machine switches from the first channel to the second channel, the circuit includes: a processor, coupled to the medium access controller MAC, to receive an indication of the handover; a random delay time circuit, coupled to the processor, to provide a random delay time (t _rwait ) in response to receiving the indication; The processor delays the switching of the transceiver relative to the time t by the random delay time (t _rwait ). 2. The channel switching delay circuit according to claim 1, wherein the transceiver comprises a base station BS of a wireless area network WRAN, and the medium access controller MAC cooperates with a cognitive radio CR to sense the occupancy of the first channel, the processor is coupled to the medium access controller MAC and the transceiver to respond at a time delayed by the random delay time (t _rwait ) from the time t The transceiver is switched upon the sensed occupancy of the first channel. 3. The circuit of claim 1 , wherein the random delay time circuit comprises: a random number generator coupled to the processor to generate a random number in response to a signal received from the processor, The processor provides the signal to the random number generator in response to the indication of the switch. 4. A medium access controller for switching a base station BS of a wireless area network from a first channel to a second channel at time t, said controller comprising a switching time delay circuit for switching said switching relative to time t while delaying a random delay time. 5. The medium access controller of claim 4, wherein the base station comprises a channel occupancy sensor coupled to the medium access controller to provide an indication of occupancy of the first channel, The medium access controller is coupled to the switch time delay circuit for initiating the switch in response to the indication of a randomly generated switch time. 6. The controller as claimed in claim 1 , comprising: at least one counter coupled to said processor, said counter defining a time window for said random delay time, said time window comprising a maximum waiting time ( _tmax ) and at least one of the minimum waiting time (t _min ), The processor is configured to randomly select a wait time from times within the time window. 7. A method for controlling channel switching in a BS of a wireless local area network, comprising the steps of: establishing a communication link between the base station and at least one CPE, the communication link comprising a first air channel; deciding to switch the communication link from the first air channel to a second air channel; generating a random number in response to said determining step; generating a time t for switching to the second channel based on the random number; announcing said time t to said at least one CPE; Switching said base station from said first channel to said second channel at said time t, wherein sensing occupancy of said second channel is performed after said determining step and before said switching step measurement steps. 8. A method for controlling channel switching of a transceiver, comprising the steps of: determining to switch the transceiver from a first channel to a second channel; switching to the second channel after a random time delay. 9. The method for controlling channel switching as claimed in claim 8, further comprising the steps of: After performing the determining step, generating a random number; Based on the random number, the random time delay is determined. 10. The controller of claim 1 , comprising at least one counter defining a time window comprising at least one of a maximum latency ( _tmax ) and a minimum latency ( _tmin ), The processor is configured to randomly select a wait time from times within the time window. 11. The controller of claim 1, wherein the base station further comprises: a channel occupancy sensor coupled to the processor, The processor is configured to select a second channel from a list of candidate channels if the channel occupancy sensor indicates occupancy of the first channel before expiration of the random wait timer. 12. A medium access controller MAC used in frequency hopping FH wireless area network WRAN, said medium access controller MAC comprising: a processor configured to select a next-hop channel for the WRAN system; a random delay time generator, coupled to the processor, to generate a random delay time in response to selection of the next-hop channel by the processor; After the random delay time expires, the WRAN jumps to the next-hop channel. 13. The controller of claim 12, wherein the WRAN further comprises a spectrum sensor coupled to the processor to sense occupancy of the next hop channel after the random time delay has expired state, and providing an indication of the occupancy state to the processor; if said indication of said occupancy state indicates that said next-hop channel is not occupied, said transmitter switching to said next-hop channel in response to said indication of said occupancy state; If the occupancy status indicates that the next-hop channel is occupied, the transmitter selects a different next-hop channel in response to the indication. 14. A node of a wireless network comprising a radio frequency transmitter operable to transmit radio signals on at least one channel selectable from a plurality of channels of a wireless transmission medium, said node comprising: a receiver operable to receive a channel switch command at the input; a random number generator coupled to the input and providing a random number in response to receiving the channel switch command; a processor coupled to the random number generator to receive the random number and provide a channel switching time based on the random number, The transmitter is configured to transmit a radio signal including the channel switching time to at least one other node of the wireless network. 15. The radio frequency transmitter as claimed in claim 14, wherein said transmitter further comprises: a memory storing at least a list of candidate channels, and The processor is configured to receive a candidate channel from the list and provide the candidate channel to the transmitter, the radio signal also including the candidate channel. 16. The radio frequency transmitter of claim 15, wherein the memory is coupled to the receiver. 17. A radio frequency receiver comprising: a radio frequency front end tunable to receive a radio signal on a channel of the transmission medium comprising a channel switching command comprising a random switching time signal; A channel switching processor, coupled to the radio frequency front end, to receive the channel switching command including the random switching time signal, and tune the radio frequency front end at a time determined by the channel switching time signal. 18. A radio frequency transceiver comprising: a radio frequency front end operable to transmit and receive signals on channels of the transmission medium; random number generator; A channel switching processor, comprising: an input terminal for receiving a channel switching command, the channel switching processor is coupled to the random number generator to receive a random number, and is configured to respond to the channel switching command based on the The above random number is used to provide a randomly generated switching time signal; The radio frequency front end is configured to transmit a radio signal comprising the randomly generated switching time signal. 19. The transceiver of claim 18, wherein the radio frequency front end comprises: a tuning circuit coupled to the channel switching processor, The processor is also configured to change the same channel based on the random time switching signal. 20. A wireless network comprising: at least a first wireless transceiver and a second wireless transceiver each comprising a radio frequency front end operable to transmit and receive radio signals over the same channel of a wireless transmission medium; The first wireless transceiver includes: random number generator; A channel switching processor, comprising: an input terminal for receiving a channel switching command, the channel switching processor is coupled to the random number generator to receive a random number, and is configured to respond to the channel switching command based on the The above random number is used to provide a randomly generated switching time signal; The radio frequency front end is configured to transmit a radio signal comprising the randomly generated switching time signal. 21. The method of claim 20, further comprising the step of selecting a channel comprising said second channel. 22. The method of claim 21, wherein the step of selecting a channel comprises the step of sensing at least a portion of the RF spectrum for channel occupancy. 23. The method of claim 21 , wherein the step of selecting a channel comprises the step of: storing a list of candidate channels in memory; A second channel is selected from the stored list of candidate channels. 24. The method of claim 21 , wherein the step of storing the list of candidate channels in memory comprises the step of: receiving at least one channel broadcast schedule from at least one source of channel broadcast schedules; compiling the list of candidate channels based at least in part on the received at least one channel broadcast schedule; The edited candidate channel list is stored in the memory. 25. The method of claim 23, wherein the step of storing the list of candidate channels in memory comprises the step of: receiving channel information from at least one user node of the network; compiling the list of candidate channels based at least in part on the received channel information; The edited candidate channel list is stored in the memory.

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